SpringBoot defaultTracingObservationHandler is not ordered as documented

The javadoc on MicrometerTracingAutoConfiguration.DEFAULT_TRACING_OBSERVATION_HANDLER_ORDER says it is a @Order value for the defaultTracingObservationHandler bean. However, in the code, this constant is not applied to the defaultTracingObservationHandler bean definition.

This PR specifies the missing @Order on the defaultTracingObservationHandler bean.

Comment From: wilkinsona

Thanks very much, @ttddyy.